The original MPlayer m_config was essentially only responsible for
handling some command line parsing details, handling profiles, and
file-local options. And then there's the new mpv stuff (that stuff was
regretfully written by me), which is mostly associated with making
things thread-safe (includes things like making it all library-safe,
instead of stuffing all option data into global variables).
This commit tries to separate them some more. For example,
m_config_shadow (the thread-safe thing) now does not need access to
m_config anymore. m_config can hopefully be reduced to handling only the
"old" mplayer-derived mechanisms.